A defence witness in the Bain retrial says Laniet Bain told him she was being sexually abused by her father.
The Crown says David Bain, 37, killed his parents Robin and Margaret and siblings Arawa, Laniet and Stephen at the family's house in Dunedin on 20 June 1994.
The defence argues Robin Bain was depressed and unstable, and killed the family present in the house before shooting himself.
Stephen Cousins employed Laniet Bain the year before the 18-year-old and four other members of her family were killed.
Mr Cousins told the High Court in Christchurch on Tuesday that, in late 1993, some girls came to him saying Laniet was trying to turn her life around and asked if he could give her a job in his dairy.
Mr Cousins said during the two or three times Laniet worked for him, she told him Robin Bain had been having sex with her in Papua New Guinea, where the Bains had worked as missionaries, and the abuse was still going on.
Mr Cousins said he told Laniet to go to the police and offered to act as her support person. However, he said Laniet told him she would go in the next few days.
The trial has been running for 43 days and there has been no evidence given of Laniet making a complaint to police about being sexually abused, or of telling anyone in her family about it.
But the defence says a suggestion that the abuse was to be revealed in June 1994 prompted the killing spree by Robin Bain.
Robin Bain a 'walking cadaver'
Earlier, a defence witness described Robin Bain as "robotic" and like a "walking cadaver".
Joan Withers, who was in charge of the Education Review Office review of the school where Robin Bain was principal, told the jury the 58-year-old was the most unusual person she had ever met, and was impassive and robotic.
"I described him to my colleague Pat as a walking cadaver because he seemed to be dead behind his eyes," she told the court. "There was just no flicker of light there."
Mrs Withers said she found no obvious curriculum being followed by Robin Bain at Taieri Beach School in 1993.
She said there were concerns about the lack of progress in the school, and revisited the school four months later.
At that time progress was found, and under cross-examination Mrs Withers said 14 of the 16 points of concern were addressed.
She acknowledged that there had been probably only three months of school time for that progress to have occurred.
But Mrs Withers did not agree with the wording of the report that followed the second review, which said "substantial" work had been done by Mr Bain, as she felt it was more of the school board's work.
Choir members give evidence
Two other witnesses to appear on Tuesday were involved in a choir rehearsal with David Bain for a production of Oedipus Rex the day before the killings.
Sarah Jones-Gallagher and Sarah Cummins said David Bain was not wearing any glasses that day, although he later told an aunt he had been wearing an old pair of his mother's spectacles that weekend.
A lens from those glasses was found in Stephen Bain's bedroom, and damaged frames and the other lens were found on the chair at the entrance of David Bain's bedroom.
David Bain denied wearing the glasses when interviewed by police and maintains it was his father Robin who was the real killer.